1. Field of the Invention
This invention relates to an original reading device in a facsimile, a digital copying apparatus, an image editing apparatus or the like. More particularly, it relates to improvements in the mechanism of a device which reads the image of an original and generates an electrical signal corresponding to the image.
2. Description of the Prior Art
A usual original reading device is designed such that an original is placed on an original table with the surface to be read thereof facing downward and the original is scanned from below the original table. However, such a device involves the cumbersome operation of covering the portion of the original which need not be read with a masking sheet or superposing a plurality of originals one upon another for synthetic reading.
An original reading device of the type in which an original is placed on an original table with the surface to be read facing upward is disclosed in German Pat. No. 30 20 258. In the device disclosed in this German patent, the original is pressed against the original table by an original keep or retention plate having a transparent plate and the surface to be read of the original is scanned from above the retention plate by the use of a mirror. The original table is formed of a cushion material having elasticity so that when a thick original such as a book or the like is placed on the original table, the original table is elastically depressed to ensure that the surface to be read is kept at a predetermined level. However, even if such an elastic original table is used, if the thickness of the original further increases, the level of the surface to be read becomes higher than the predetermined level and the original retention plate and the scanning mirror become inclined relative to the surface to be read, which makes accurate reading impossible, or the length of the optical path between the surface to be read and the lens varies, also making accurate reading impossible.